In radio communications, transmit data is generally encoded before transmission in order to improve error correction capability. One example of such encoding is the use of an LDPC code such as described in Non-patent Document 1. This LDPC code enables error correction to be performed using an extremely large block unit (constraint length), and is therefore considered to be resistant to burst errors and suitable for communications in a fading environment.
Also, a multi-antenna transmitting apparatus that transmits OFDM signals from a plurality of antennas, such as described in Non-patent Document 2, is known as a technology for improving data transmission speed. With this kind of multi-antenna transmitting apparatus, interleaving data in the frequency direction (subcarrier direction) has been proposed as one method of suppressing burst errors due to frequency selective fading.
FIG. 1 shows an example of the frame configuration of a transmit signal in this kind of multi-antenna transmitting apparatus. In FIG. 1, a preamble for estimating distortion due to fading fluctuation—that is, channel estimation—and frequency offset between the transmitter and receiver are placed at the head of a frame, followed by data symbols. Also, pilot symbols for estimating frequency offset that fluctuates overtime are placed in carrier Y. One square in FIG. 1 represents one symbol. That is to say, in the example shown in FIG. 1, one OFDM symbol composed of a total of 7 symbols (data symbols and a pilot symbol) is transmitted at each of times i, i+1, . . . . At this time, data is interleaved and placed in (1) (2) (3) . . . (11) (12) order within one OFDM symbol.
Non-patent Document 1: “Low Density Parity Check Encoding and Decoding Method, LDPC (Low Density Parity) Encoding/Sum-Product Decoding Method” Triceps 2002Non-patent Document 2: “High Speed Physical Layer (PHY) in 5 GHz band” IEEE802.11a 1999